In recent decades achievement of efficient and relatively inexpensive electrical energy production has become a major concern. Of the various types of power plants, coal-burning plants have been particularly popular and widely used. The reasons for this include relative adaptability to a variety of locations and relatively wide. availability of a comparatively inexpensive fuel.
A problem with conventional coal burning systems involves the general methodology of fuel use. In a typical system the coal is simply burned, with the waste discarded. This has generated two substantial concerns. First, coal fuels often include therein relatively useful organic fractions, which could be isolated and refined to useful oil products, such as diesel fuel or the like. Typically in conventional plants these fractions are merely burned, as an inexpensive fuel, along with the remainder of the coal. It is readily seen that this, arguably, is an inefficient utilization of the coal as a natural resource.
Secondly, conventional systems generally require a relatively high grade of fuel coal. For example, coal having a substantial amount of sodium therein is not readily utilizable, as it does not burn well. If such materials in the coal were first extracted therefrom, a lower grade coal could be effectively used as a fuel source.
Methods of coal liquefaction, i.e. the removal of volatile materials from coal, are well-known. Generally, however, such processes have not been practiced on coal to be utilized as a fuel for power generation. A major reason for this is that the resultant coal char has not been a desirable fuel. While such char has a significant energy content, it generally does not burn well and cleanly in conventional boilers. Thus, the use of char has been resisted by power companies.
Coal, typically in the form of metallurgical coke, is also utilized in the steel-making industry, for example to reduce oxides of metals such as iron. In one known process, coal products are pelletized with water, silica, burned limestone and taconite, and are treated in a high temperature oven such as a cupola. The pelletization step is generally conducted in an autoclave. To date, this method of generating metallic iron has received minimal attention.
What has been needed has been a more efficient method of energy production, utilizing, as the ultimate source of fuel, coal and coal products. More particularly, what has been needed has been a method of energy production wherein values other than simply crude fuel values of the coal fuel are more efficiently and effectively utilized, for example in iron refining and boiler operation. A particularly useful process would be one in which steel production occurs, as a by-product to energy generation.
If iron were to be reduced under pressures greater than atmospheric, the efficiency would arguably be increased as output gases have a greater energy content which can be extracted to generate electricity. Thermal efficiency would also be increased and higher gas concentrations and faster reaction rates would be obtained, thereby resulting in better overall reduction. A high pressure cupola would require smaller containers for output gas purification, thereby allowing for off-site assembly and much lower cost. The use of pressurized reduction has been avoided in the past, at least in part because molten metals under pressure present special handling problems.
When iron oxides are reduced in the presence of carbonation materials, molten iron and slag are produced. The slag has generally been considered a waste product. However, if it is produced in a large scale operation, handling of the slag can involve considerable expense. It would be preferred to have an overall system designed for an efficient handling of any slag material generated in a reduction furnace.